I guess it could be assumed that NW is the passive investor but since this is basically a press release from Airtran (not ATA) it was not specifically stated.

If that is the case than it would be a wise move by NW. Similar to moves they have made in the past with both KLM and CO. At one point KLM bought a minority stake in NW to help them stay afloat and then later sold it, after that NWA bought about 17% of CO stock partly to help them out, and partly to have control over proposed mergers of CO with other carriers. They both worked into very seamless Code shares without many concerns from the DOT. NWA has since sold its share in CO.